State police said they are investigating an incident involving the warden of Garner Correctional Institution receiving a "threatening letter" on April 1.

The letter stated a threat to harm state Department of Correction staff and also inmates at the high-security prison at 50 Nunnawauk Road, state police said.

State police said that the letter apparently was sent to the warden by a Garner inmate.

Garner, which opened in 1992, specializes in treating inmates with chronic mental health problems.

State Trooper First Class Donald Chasse is investigating.